Effect of deformation ratio of flow-induced crystallization on polyethylene in crystalline behavior, thermal stability, and tensile loading: A molecular dynamics simulation

Abstract

Since the physical and mechanical properties of semicrystalline polymers strongly depend on crystalline morphology, understanding the correlation between the crystallization kinetics and crystalline structure of polythene is beneficial for their rational processing and applications. In this study, united-atom (UA) molecular dynamics (MD) simulations were employed to elucidate the variations in crystalline structure, phase transition temperatures, and uniaxial tensile deformation among polyethylene (PE) with randomly oriented and flow-induced crystallization (FIC). The results showed that crystallization occurs in areas with low potential energy. For the FIC process, the entanglement parameter and interplanar spacing was less than for randomly oriented crystallization, and the crystallinity was higher. The relationship between the deformation and the crystallinity of PE with randomly oriented crystallization was expressed, which indicates that the crystalline structure promoted elongation at break of PE in tensile deformation. As PE was oriented to crystallize during the FIC process, the polymer stiffness is positively correlated with the deformation ratio of the PE model, so crystal conformation systems with higher deformation ratios produce higher ultimate stresses in tensile loading. From the visualization results, the crystalline phase was stable and does not easily transform into an amorphous phase during tensile loading. Additional results show that the fracture region of PE at tensile fracture tends to develop in the amorphous phase under tensile loading. Energy analysis showed that the elastic and yield regions were mainly dominated by intra-chain bonds, angles, and dihedral motion of PE, whereas interchain nonbonded interactions mainly dominated strain-hardening regions.